Silicon oxide layers may be formed by deposition on or thermal oxidation of a silicon-containing substrate. For thermal oxidation the silicon-containing substrate is subjected to a heat treatment at temperatures between 800° C. and 1200° C., wherein dry oxidation uses molecular oxygen and wet oxidation uses water vapor as oxidant. Since impurities dissolve differently in silicon and oxide, thermal oxidation may result in that the growing silicon oxide absorbs impurities from the silicon-containing substrate. Deposited oxide, on the other hand, typically shows lower density and less conformity.
There may be a need for providing enhanced methods for forming a silicon oxide.
Further, new generations of power devices follow vertical architectures (e.g., trench power Metal Oxide Semiconductor Field Effect Transistors (MOSFETs)). These vertical power devices are using a trench for gate formation with an aspect ratio (AR) that is typically about 3:1 (but can be as high as 12:1. The challenge for those structures is the conformal formation of a high-quality gate oxide. Some aspects of a high quality gate oxide are the low gate leakage at large blocking voltage, the gate oxide is sustaining a high electric field and high reliability.
There may be a need for providing enhanced methods for forming a gate oxide.
In addition, the oxidation of surfaces of silicon carbide wafers has been difficult to achieve. Presently, it is usual practice to deposit chemical vapor depositions (CVD) oxides on the surface of the silicon carbide wafers in order to generate gate oxides, although the oxide quality and the quality of the gate oxide/silicon carbide interface is subject to severe restrictions, depending on the heat treatment method used, owing to the defects in the oxide layer and at the interface. CVD oxides are significantly lower in quality (e.g., the maximum permissible electric field in the gate oxide for a defined reliability) than oxides generated by a thermal oxidation procedure.
The heat treatment processes used at present requires the use of nitrogen monoxide or nitrogen dioxide, which on account of their toxicity or, respectively, their fire-promoting properties, necessitate particular effort and expense in their provision (e.g., double-wall piping, gas alarms, etc.).
The number of interface states can be reduced by means of a plasma-enhanced chemical vapor depositions (PECVD) SiN interlayer, but in this case as well it is necessary to employ a heat-treatment step with NO or N2O.
Thus, there may be provide a method allowing SiO2 layers for gate oxides to be produced on silicon carbide wafers with high quality at acceptable effort and expense.